Method of improving the operation of a cupola



United States Patent 3,410,930 METHOD OF IMPROVHNG THE OPERATION OF ACUPOLA Thomas E. Barlow, Deerfield, Ill., assignor to InternationalMinerals & Chemical Corporation, a corporation of New York No Drawing.Continuation of application Ser. No.

227,699, Oct. 2, 1962. This appiication June 4,

1965, Ser. No. 461,496

2 Claims. (Cl. 264-450) This application is a continuation applicationof my copending application Ser. No. 227,699, filed Oct. 2, 1962, nowabandoned.

This invention relates to improvements in refractory compositions andtheir use. In its major aspect the present invention relates to dense,acidic refractory compositions suitable for use in ladles for molteniron or steel, cupola linings, taphole plugs, runners, and otherstructures subjected to the corrosive action of molten metal and theslag carried with the metal. In another of its aspects this inventionrelates to improvements in the operation of cupolas obtained by the useof an improved monolithic refractory lining therefor. In still anotherof its aspects this invention relates to a method for inhibiting thesubsurface formation and penetration of FeO in dense, acidic refractorylinings.

In cupola operation and in ladles handling ferrous metals such as grayiron, steel and malleable, there is a problem of FeO formation and thedeleterious effects which it has, particularly upon refractory linings.The amount of such formation depends upon the situation. For example, inthe cupola, the oxide formation is very rapid because of the presence offree oxygen moving at a high speed past the refractory Wall. In the caseof a ladle, again the formation of oxide is high because of the presence of liquid metal in contact with the lining. After the ladle hasbeen emptied, there is still a film of liquid metal retained on thelining. At such high temperatures this film of liquid metal oxidizesrapidly and forms FeO. Therefore, although the conditions are differentin a cupola than in a ladle, the problem is essentially the same butthrough a slightly different mechanism. In a cupola there is very littlemetal in contact With the refractory but the rate of oxygen flow in thatarea is so great that it will oxidize even nonliquid iron and provideFeO. In the case of a ladle, there is less oxygen, but there issufficient to rapidly combine with the metal film left in the ladleafter it is emptied. It is a major object of the present invention tominimize the formation and prevent the penetration of these FeOmaterials into the refractory, thus destroying the refractory.

It has been determined that the greatest destruction of the refractoryoccurs through the subsurface formation and subsequent penetration ofmetal oxides such as FeO which combine rapidly With the normal SiO A1 0compositions of conventional dense acid linings. The FeO content forms aternary of low melting temperature which rapidly penetrates into thepores of the refractory, thereby causing further destruction andcompounding. I have found that the inclusion of certain materials in thedense 3,410,930 Patented Nov. 12, 1968 acidic refractory composition,either in combination with carbon or Without carbon, will prevent theseFeO formations from occurring below the surface of the refractory. As aresult, the melting point of the refractory remains high and losses aredrastically reduced. To a certain extent a similar effect is experiencedwhen carbon is added by itself but the effect is minor because of thefact that carbon oxidizes readily to CO and is lost. The loss of thecarbon leaves voids in the refractory which, in turn, reduces itsrefractory value. In contrast to this my materials are not destroyedreadily with oxygen but rather remain intact to prevent the suburfaceformation and consequent penetration of FeO. Furthermore, the carbon byitself reduces the fusion ability or ceramic bond characteristics ofmonolithic, unfired refractories. Therefore, they have not beenacceptable in unfired refractories because they create a Weak, friableWall. I have found that the presence of my materials permits carbon tobe useful in these conditions first, because it prevents the oxidationof the carbon to C0 and also because it maintains vitrification anddepth of fusion Which is superior to that obtained Without my materialsand Without the carbon. In other Words, my materials actually increasethe strength and the depth of fusion of the unfired refractory and morethan compensate for and eliminate the deleterious effect of carbon.

In a cupola this has importance beyond just improving the refractorinessby eliminating the penetration of the FeO. In commercial operation asthe FeO penetrates the refractory and reduces its fusion temperature, itthen fluxes the refractory from the wall and permits it to move downinto the Well of the cupola in high volumes. This slag moving into theWell of the cupola has, because of the penetration of FeO, a highpercentage of FeO in its make-up. By analysis, for example, it has beenfound that slags on the wall of the cupola to a measurable depth Willc0ntain about 8 to about 15% FeO. These slags move into the well of thecupola and then are removed from the cupola through either the slag holeor the tap hole. Prior to the time that they are removed, however,molten metal drops through the slag blanket. The presence of highpercentages of FeO at this point immediately starts robbing the moltenmetal of both silicon and carbon. As a result, definite silicon lossesand carbon losses take place at this time. This is demonstrated also bythe fact that the slag as it is removed from the cupola, instead ofhaving 8 to 15% FeO, may be down to 0.5% or 1%. The FeO content of theslag has been reduced by the action of the silicon metal in the moltenmetal coming through the blanket of slag. Therefore, in a cupola, arefractory lining which resists FeO penetration also reduces the amountof FeO content in the slag blanket. In this manner there is anelimination or drastic reduction in the necessity for reduction of FeOby the molten metal and thereby an in crease in the silicon content ofthe metal as Well as the carbon content. These changes in thecomposition of the metal have important significance in the operation ofthe cupola. For example, reductions in the coke, silicon and limestonein the charge permit greater operating economies. Also, betterregulation of temperature and silicon and carbon contents in the meltare possible.

In the ladle, a similar situation takes place, but there is enoughdifference to require some explanation. In this case, as the ladle isemptied the film of molten metal oxidizes rapidly leaving a film of FeO.This film penetrates into the lining, thereby reducing itsrefractoriness. However, even more important in this case, is the factthat this penetration of FeO permits larger quantities of FeO to beretained by the ladle wall. When the ladle is refilled (and commonpractice is to refill it many, many times), the molten metal coming intothe ladle immediately picks up the FeO off of the wall and carries it asan undesirable slag. This material being carried by the molten metalfrom the ladle into the mold and mold cavity creates defects in thecastings which may show up as ceroxides or, in foundry nomenclature,pinholes and snotters. It is extremely desirable to keep these ladlesclean or free of such iron oxide formations. My refractory linings, whenused in ladles, prevents the formation of FeO in excess quantities andthereby minimizes this problem.

It is, therefore, an object of the present invention to provide animproved dense acidic refractory composition suitable for use as liningsin cupolas, in ladles for molten iron or steel for taphole plugs andother structures subjected to corrosive and erosive action of moltenmetal and the slag carried with the metal.

It is another object of this invention to provide a method forinhibiting the subsurface formation and the penetration of FeO in denseacidic refractory linings.

It is a further object of this invention to provide improvements in theoperation of cupolas obtained by the use of an improved monolithicrefractory lining therefor.

Additional objects of the present invention will be apparent from thedescription which follows.

In accordance with the present invention I have .dis covered that theobjects of this invention can be accomplished by including in a denseacidic type refractory composition from about 2 /2 to about by weight,preferably between about 4 and 8%, of a reductive element which ischemically and thermodynamically capable of deoxidizing FeO attemperatures in the range of about 1800 F. to about 3000 F. to produce anonalkaline refractory oxide. Examples of such metals include silicon,aluminum, chromium, manganese and the like. These metals may be employedeither as the commercially pure metal or as alloys such as ferrosilicon,ferromanganese, ferrochrorne, aluminum-silicon, chromium-silicon,manganese-silicon and silicon-carbide and other commercially availableforms of said reductive metals. When employed as alloys it is preferredthat the reductive metals be present as the major component as forexample, 5098% silicon in the ferrosilicon form. It will be understoodthat the weight proportion recited hereinabove refers to the weight ofreductive metal component so that when alloys or other metallo-carbonforms are used, allowances for their nonreductive metal content can bemade. Experience has indicated that the metallo-carbon forms such assilicon carbide, generally do not function as well as the free metal atlower operating temperatures.

My improved refractory composition may also, optionally, contain up toabout 15% by weight of carbon which may be in the form of graphite,finely divided coke, sea coal, petroleum, pitch and the like. As pointedout hereinabove, the reductive metal component in combination with thecarbon prevents the rapid oxidation of the carbon to CO with itsconsequent loss, and also maintains a vitrification and depth of fusionin the refractory which is superior to that obtained without the use ofthe reductive metals and without the carbon.

In its broadest aspect the present invention comprises a dense acidicrefractory composition containing from about to about 80% by weight ofconventional fire clay, from about 20 to about by weight of silica sand,from about 2 /2 to about 15% by weight of a reductive element chemicallyand thermodynamically capable of reducing FeO at a temperature in therange of 1800 to 3000 F. to form a nonalkaline refractory oxide, andfrom 0 to about 15 by weight of carbon. The reductive material ispreferably selected from the group consisting of silicon,silicon-carbide, aluminum, chromium, manganese, ferroalloys of theforegoing, and mixtures and alloys of the foregoing. It will beappreciated that the iron in such alloys is merely a diluent and servesno chemical or refractory purpose in the composition.

In a preferred embodiment the refractory composition of the presentinvention contains about 40% by weight of fire clay, about 50% by weightof silica sand, about 5% by weight of carbon and about 5% by weight ofsilicon metal.

In the preparation of these compositions the individual ingredients arepreferably in finely divided form, viz., having a mesh size below about/a inch and preferably between about 20 and 200 mesh. The individualingredients can be mulled in conventional mixing equipment and appliedas monolithic linings in cupolas, ladles or the like, using conventionalpatching and ramming guns.

lternatively, the mixture may be formed into bricks of any desired shapeand fired at ordinary firing temperatures, for example, from about 1800to about 2400 F. for periods of from about 12 to about 24 hours.

It is important in the practice of the present invention that therefractory composition not contain significant amounts of materialswhich are capable of consuming by side reactions the reductive metalcomponent present therein. For example, the refractory compositionshould not contain such things as magnesite, or limestone or otheralkaline metals which would be reduced by reductive metal either duringthe use of said refractory or in the firing of the same as in the casewith bricks. With bricks it is recognized that a certain amount of thereductive metal is consumed in the firing process. Hence, when therefractory composition is intended for brick making, it is desirable touse an excess amount of reductive metal and to adjust the firing step sothat the final brick composition contains the reductive metal in aproportion within the range recited hereinabove. Alternatively, twodifferent metals can be used, such as silicon and aluminum, one of whichmay be consumed in the firing step.

The refractory compositions of the present invent-ion are to bedistinguished from other refractories which have in the past includedreductive metals. The present refractory compositions are dense andacidic in character as opposed to either porous and insulating oralkaline in character. For example, aluminum metal has been included inbrick manufacture for use as a blowing agent to increase the porosityand lessen the density of the resulting brick thereby improving itsinsulating capabilities. In such instances all but a minor amount of thealuminum is consumed in performing its function. The refractorycompositions of the present invention do not function primarily asinsulating materials. Indeed, as employed in cupolas and in ladlelinings it is important that they pass the heat rather than retain it inorder to avoid damaging the furnace or ladle.

It is significant to note that the composition of the present inventionserves a dual function which is both chemical and ceramic. From aceramic standpoint one would not add a reductive metal to the refractorycomposition since these materials are known to have a deleterious effectupon the refractoriness of the composition. I have found, however, thatthe chemical benefit contributed by the reductive metal component morethan offsets the deleterious effect upon the refractoriness of theresulting composition. That is, I have recognized that the chemicalreactions taking place in a cupola or a ladle at the surface and belowthe surface of the refractory lining cause by far the greater amount ofdamage to said lining than the chemical effects of heat and physicalerosion. Thus, by the inclusion of a reductive metal in a dense acidicrefractory composition, I have been able to minimize refractory lossthrough subsurface FeO formation and the fluxing of the refractorylining caused thereby.

The following examples are intended to illustrate the underlyingprinciples of the present invention and are not to be construed asunduly limiting thereof.

EXAMPLE 1 A series of tests were made to determine:

(1) Confined expansion and hot strengths of cupola lining refractoriescontaining various amounts and grades of silicon-carbide, and

(2) The effectiveness of ferrosilicon and silicon-carbide additions to acommercial cupola refractory (Cupoline 77) against slag penetration. Theconfined-thermal expansion and hot-strength propertiesof specimens ofthe various refractory materials were determined according toAFS-recommended procedures for testing same. The composition, expansioncharacteristics and hot strength of the various refractories are listedin Table l.

also had considerably higher hot strength than did the othercompositions.

In the test for the evaluation of the effectiveness of ferrosilicon andsilicon-carbide additions to the cupola lining composition, standardspecimens 1 /2" in diameter by 2" long were made of the variousrefractory materials. Each specimen had a center cavity molded into oneend. The center cavity was deep and /s" in diameter with a hemisphericalbase. Two types of slag were employed. The composition of the slags was:

1) A mixture of cupola slag and iron oxide ground to -70 mesh in theproportion of 85% slag and 15% foundry-grade iron oxide (Fe O (2) Amixture of iron oxide and carbon composed of 90% foundry-grade ironoxide and 10% carbon ground to 70 mesh. It was intended that the carbonand iron oxide would react when heated to give FeO and CO.

The hole in the dried specimen of the refractory was filled with 1.00gm. of the powdered slag mixture. The refractory specimen was chargedinto a dilatometer at 2500 F., held at 2500" F. for 10 minutes, heatedto 2700 F. in about 10' minutes, held at 2700 F. for 12 minutes andremoved from the furnace. The specimen was cooled, broken lengthwise andexamined for slag attack. (The amount and composition of the slag andthe heating rate TABLE 1.-CONFINED EXPANSION AND HOT STRENGTHS OFCUPOLA- LINING REFRACTORIES CONTAINING SILICON CARBIDE 1 MixtureComposition, percent:

Lawco Clay 23 23 23 23 23 23 Clarion Clay 19 Davis Sand (AGF48) 53 SiC,85%, 100 Mesh- SiO, 85%, 10 Mesh.-. SiC, 97%, 100 Mesh.

1. 75 1. 95 1. 65 l. 85 l. 10 l. 0. 0. 60 0. 40 0. 70 0. 95 -0. -2. 100. 2. 95 0. 85 2. 95 1.05 2. 95 --l. 45 2. 95 1.

1 All samples confined in quartz tubes. 2 Same composition as Mixture254 but another mixture. 3 Dust-collector fines.

It will be seen that the best results were obtained with mixture 258which contained 5% of silicon-carbide from the dust collector. Aconsiderable portion of the dust given appeared to give better resultsthan did various other conditions which were tried.)

The composition of the various refractory mixtures collector fines wasbelieved to be -325 mesh. Mixture 258 evaluated in the slag-penetrationtest is listed in Table 2.

TAB LE 2.COMPOSITION SLAG PENETRATION OF CUPOLA-LINING REFRACTORIES USEDTO EVALUATE Mixture FeSi, 90% Si,

FeSi, 98% Si, -100 FeSi, 50% Si, 100

S10, 85% SiO, 100 Mesh.

Water The results obtained when samples of Cupoline 77 containing 3, 4,5, 6, and of 75% ferrosilicon using the mixture of 85% of cupola slagwith of iron oxide showed that the slag penetration was severe inCupoline 77 and progressively decreased in severity as the ferrosiliconcontent increased. Small differences in the amount of penetration couldbest be determined by observing the number of pinholes on the insidesurface of the slag cavity in the refractory. The number of pinholesdecreased as the penetration decreased. This test appears sensitiveenough to show the difference of refractories containing 4 or 5% offerrosilicon.

The results obtained when Cupoline 77 samples containing 0, 5 and 10% of75 ferrosilicon were tested with the iron oxide-carbon mixture were notas distinctive as those obtained when the cupola slag-iron oxide mixturewas employed because the former tended to boil.

The efiect of the addition of various grades of ferrosilicon to theCupoline 77 on slag penetration was also observed. Samples of Cupoline77 contained 5% of 50,

EXAMPLE 2 A number of dense acidic refractory compositions containingferrosilicon, silicon, aluminum, graphite, pitch in various proportionswere prepared and evaluated to determine their confined expansion andhot strengths, according to American Foundrymens Society recommendedprocedures for testing molding sand. All samples were confined ingraphite tubes while determining thermal expansion. The results of thesetests are set forth in Tables 3 and 4.

TABLE 3.PROPERTIES OF LADLE REFRACTORIES Sample Composition, percent:

Revivo clay (42) (24) (20) (22) 22 22 22 22 Western Bentonite. (1) (l)(2) 2 2 2 2 Davis Sand 51 52 49 Ferrosilicon, Mes

Silicon, 98%, -200 Mesh.

Aluminum, Alcoa 101, l00 Mes Silica Flour, -200 Mesh phite (JacksonGlutr'm (50% Solids)...

Pit h 2 Sandy Revive.

8 Caroline.

3 Fluid coke 6 percent; graphite 6 percent, total 12 preeent. Templine.Electroline. 11 CLL30. l2 CLL25.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,410,930 November 12 1968 Thomas E. Barlow It is certified that errorappears in the above identified patent and that said Letters Patent arehereby corrected as shown below:

Columns 5 and 6, TABLE 1, second column, line 11, "-1.90" should read-0.90 Columns 7 and 8, TABLE 2, first column, fourth item "FeSi, 75%"should read FeSi, 75%- Si "7 same column, TABLEB, first column underExpansion, percent, third item "llOO F. should read lOOO F. same table,under Expansion, percent, seventh column, line 4 thereof, O. 30" shouldread +0.30 same column, line 7 thereof, "+0.55 should read +0.85

Signed and sealed this 10th day of March 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents

1. A METHOD OF IMPROVING THE OPERATION OF A CUPOLA WHICH COMPRISES LINING SAID CUPOLA WITH A MONOLITHIC UNFIRED DENSE ACIDIC REFRACTORY COMPOSITION CONTAINING, IN FINELY DIVIDED FORM, AND IN SUBSTANTIALLY HOMOGENEOUS ADMIXTURE: (A) FROM ABOUT 20 TO ABOUT 80% BY WEIGHT OF FIRE CLAY; (B) FROM ABOUT 20 TO ABOUT 80% BY WEIGHT OF SILICA SAND; (C) FROM ABOUT 0 TO ABOUT 15% BY WEIGHT OF CARBON; AND (D) FROM ABOUT 2 1/2 TO ABOUT 15% BY WEIGHT OF SILICON METAL. 